Efficient laser ablation on flat and cylindrical surfaces

Efficient Laser Ablation on Flat and Cylindrical Surfaces Machining using short and ultrashort laser pulses is vastly used in science, technology and medicine. However, how to use the expensive laser radiation efficiently is an important question. Laser ablation rate depends on various parameters, such as: scanning speed, laser power and pulse repetition rate. In this work, using a theoretical model and two experimental methods, optimal parameters for efficient laser ablation on flat and cylindrical surfaces of copper were found. Experiments were carried out to find the most optimal distance between laser pulses, as well. According to the theoretical model there is an optimal fluence at which material is removed most efficiently. Pulse energy was changed in order to find the optimal point. Rectangle shaped cavities were ablated on a flat copper sample using nanosecond laser and their depths, widths and surface roughness's were measured. This experiment was performed at different pulse repetition rates and various beam scanning speeds, while changing laser power to keep the pulse energy constant. Using a picosecond laser, efficient laser ablation on cylindrical copper samples was also measured. In this experiment the spinning cylindrical copper samples were ablated by the laser. The ablated volumes and surface roughness’s were measured. The experiment was repeated at various pulse repetition rates. In both experiments the optimal fluence interval was found 4 – 8 J/cm2. The most efficient scanning speeds for 10, 20, 30 and 40 kHz were 10, 20, 30 and 40 mm/s, respectively. It corresponds to the 1 μm distance between laser pulses on sample surface. It was shown, that using optimal laser fluence and scanning speed not only yields the highest ablation rate, but lowest surface roughness as well. Using this method, two most significant laser processing parameters are optimized at once. During the second experiment high repetition rate laser pulses were used. The results correlated well with the theoretical model at low fluence 1 10 J/cm2, but at fluence higher than 10 J/cm2 particle shielding effect reduced experimental efficient ablation compared to the theoretical model